I'm not a macanic at any means but I found out what my problems was after 2 different garages looked at my ford freestar 2005. My van has been in so many times I guess one of the time they disconnected my air filter assembly and the little vent channel connected to the right of it. When they are seperated and you turn the stering wheel it make a thump noise. Once I found the channel loose and re-connected it the thumping stopped. If that is the problem you might need to take out the front driver light assembly to be able to reconnect it. Hope that helps I'm happy.